In many conventional computer networks, a connection between two nodes includes only a single transmission medium. Time-division multiplexing (TDM) combines multiple data streams into one signal, thereby allowing the data streams to share the single transmission medium. More specifically, as its name suggests, TDM divides the signal into a number of segments, each constituting a fixed length of time. Because the sending node assigns data to the segments in a rotating, repeating sequence, the receiving node may reliably separate the data streams at the other end of the transmission medium.
With the rapid development of modern packet-switched networks, TDM-based protocols such as Synchronous Optical Networking (SONET) have gradually fallen out of favor as a preferred technology and have been widely replaced by packet-based protocols, which transmit data over less expensive Ethernet links. For example, Voice-Over-Internet Protocol (VoIP) services have replaced many TDM-based services, given VoIP's flexibility, ease of implementation, and reduction in costs. Unfortunately, transitioning to packet-based protocols requires a service provider to incur significant expenses in expanding its infrastructure and replacing customer premises equipment.
Given the large initial investment, many service providers have been reluctant to make the transition from TDM-based services to corresponding services in packet-switched networks. TDM pseudowires allow service providers to gradually make the transition to packet-switched networks, eliminating the need to replace TDM-based equipment and drop support of legacy services. In particular, on the ingress end of a TDM pseudowire, a network element converts the TDM signals into a plurality of packets, then sends the packets across a packet-based path, or pseudowire. Upon receipt of the packets, a network element on the egress end converts the packets back into TDM signals and forwards the TDM signals towards their ultimate destination.
Although TDM pseudowires offer flexibility and reduce expenses, they also introduce problems specific to packet-switched networks. Unlike TDM connections, packet-switched networks are not designed for network-wide synchronization of nodes. Thus, although pseudowires can exchange timing information using packets, the inherent characteristics of the packet-switched network affect the accuracy and reliability of the synchronization. For example, unlike circuit-switched networks, packet-switched networks use variable paths with a variable bit rate, such that timing packets may arrive at nodes at varying intervals or may not arrive at all, thereby affecting the synchronization of the nodes.
Given these problems, many service providers express considerable skepticism regarding the viability of switching their TDM circuits onto packet-based services that emulate such circuits. One reason for such skepticism is the lack of a reliable mechanism for monitoring the synchronization of the nodes in the packet-switched network. More specifically, there is currently no known solution that allows service providers to reliably and efficiently monitor the timing information used by nodes that emulate TDM services in a packet-switched network.
For the foregoing reasons and for further reasons that will be apparent to those of skill in the art upon reading and understanding this specification, there is a need for a mechanism that reliably and efficiently monitors the timing information used by nodes that emulate TDM services in a packet-switched network.